Collapse at Ground Zero

Initially, the test seemed routine. At 9 a.m., Department of Energy (DOE) engineers detonated a nuclear bomb 1,168 ft. beneath the arid landscape of the Rainier Mesa at the Nevada test site 93 miles northwest of Las Vegas. About three hours later, after instruments detected no radiation at the site, workers in white coveralls returned to trailers near the blast area to begin collecting data. They had just started to snip the 150 cables connected to underground sensors when the earth gave way. “I felt the earth shake, and before I knew it I was standing on my head,” said J. L. Smith, a site supervisor. “We were walking on the ground, and all of a sudden it wasn’t there.”

Last week’s cave-in left a D-shaped crater about 60 ft. wide, 150 ft. long and between 10 and 30 ft. deep. Although apparently no radiation had leaked, 14 workers emerged with broken bones and lacerations. Craters from previous underground nuclear tests pock the desert floor elsewhere on the 1,350-sq.-mi. site. But officials said they had had no reason to expect such a result in the mesa because it is made up of hardened volcanic ash and granite. In the past 20 years, the Government has exploded 45 nuclear devices with no ill effects in the tunnels bored under the mesa. Indeed, until last week there had been no direct injuries from the more than 600 atomic tests conducted in Nevada since 1951.

The Soviet Union promptly denounced the explosion as a violation of a 1974 Soviet-American agreement that limits underground detonations to 150 kilotons (150,000 tons of TNT). Although the force of the weapon tested last week was classified, DOE officials said it was considerably lower than 20 kilotons, the explosive yield of the bomb dropped on Nagasaki. The blast registered 4.5 on the Richter scale on seismographs at the University of Nevada, Las Vegas. But DOE officials said the instruments probably gave a high reading because the test was conducted in hard rock, which sends out a more powerful seismic ripple than does sandy soil. The incident is not expected to interfere with future nuclear testing.